Process of producing cellulose from wood and other cellulose containing material and apparatus therefor



Jan. 1, 1935.

o. KREISSLER' 1 986,760

PROCESS OF PRODUCING CELLULQSE'FROM WOOD AND OIHER CELLUNOSE CONTAINING MATERIAL AND APPARATUS THEREFOR Filed-Feb. 17, #1934- LOTTO KREISSLER Attorney In uentoh:

Patented Jan. 1,1935

UNITED STATES i 1,986,760 I raocnss or raonucme c'ELLULosE mom WOOD AND OTHE B CELLULO SE CON- .TAINING MATERIAL AND APPARATUS macros.

om Kreissler, Frankfort-on-the-Main/Grieshelm, Germany, assignor Corporation, New York, N.

New York to American Lurgi Y., acorporation of Applicatign ggbruary 17, 1934, Serial No. 711,648

11 Claims.

and uniform impregnation of the wood chips,- or the like. In one proposal, an attempt was made to assist the penetration of the digestion liquor by cutting the wood into extremely small pieces, for instance, pieces having a length of about 25 to 40 millimeters, a-width of 20, to 35 millimeters and a thickness from 4 to 8 millimetersv wereused. These small world pieces were digested in the usual way and the liquor had to penetrate slowly from the edges of the chips. In connection with these tests, it was found that of the usual cooking time of about 12 to 15 hours, about 70% to 80% (9 or 10 hours) were required for the impregnation of the wood chips and the remaining time was required for the digestion-of the wood into cellulose. when these pricr'procedures'were carried into practice, the digestion liquor reached the middle of each wood chip at approximately the end of the cooking period. Thus, the cellulose fibers are digested on the outside of the chips and as impregnation proceeds towards the middle of the chip,'the digestion progresses approximately proportionally to the speed of impregnation. The digested cellulose o fibers, therefore, remain for many hours in the hot digestion liquor until the last cellulose fibers remaining in the inside of the wood chips have been decomposed. It has been established that the longer the retention of the digested cellulose fibers in hot liquor under pressure, the more fibers are attacked, weakened and their physical pro perties are changed. Various other attempts have been made,to provide an improved process. Among these attempts may be mentioned, the complete covering of wood to be digested with cold or hot liquor with vacuum or with pressure and dra'ning the excess liquor and then cooking in the usual way. It has also been attempted to suck the air from the disaster and the wood con.- tained therein before introducing the digesting liquor into the digester. Then again, a-procedure has been proposed which involves lixiviating the v v fibrous material in the digester and arm increasing the cooking pressure bythe'addition of steam to draw ofla part ofthe liquor for the purpose consideration has been given thus far to rapid rmany February 18, 1933 of decreasing pressure. The top valve of the digester sometimes was open in order to let out the air present at the top of the digester. The various proposals and attempts which have been made possessed disadvantages and shortcomings of one sort or another. As far as I am aware the art has? not been'provided with a process whereby uniform impregnation has been obtained and uniform cellulose has been produced. I

I have discovered a process which avoids the disadvantages and shortcomings of the prior art and which provides the art with effecting relatively uniform and rapid impregnation of the wood chips and the production of relatively uniform cellulose.

It is an object of the present invention to provide a process of digesting wood and other cellulose-containing fibrous material in an efficient, practical and economical manner.

It is another object of the invention to provide a process of digesting wood and the like in a shorter time and with the consumption of a smaller amount of steam and digesting liquor than was necessary heretofore.

" It is also within the contemplation of the invention to provide an apparatus for carrying the improved process into practice on a commercial and industrial scale.

A further object of the invention is the provi-. sion of the process for the digestion of wood and other cellulose-containing fibrous material in which the impregnation of the individual wood chips is accomplished in a relatively rapid manner and the digestion of the cellulose fibers is efiected in practically the same period of time to give improved and uniform results.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction which:

Fig. 1 is an elevational view somewhat diagrammatic of an embodiment for carrying the present invention into practice; and

Fig. 2 is a modified embodiment of the apparatus shown in Fig. 1 to carry a modified procedure of the present invention into practice. v

Generally speaking, the largest part of the the process for 1 with the drawing in volume within a pulp digester, or the like, is 00- v the foregoing air has been removed, I have found that impregnation proceeds with greater rapidity than heretofore known. With rapid impregnation, the digestion proceeds quicker andmore uni-'- formly than was possible with prior procedures.

The amount of steam and of digesting liquor required for effecting the digestion of the wood chips or other cellulose-containing fibrous material has been found less than formerly required. Due to the fact that practically all of the fibers within each individual chip is cooked or digested at approximately t e same time, practically no decomposition of cellulose fibers occurs due to the finished fibers remaining in the hot liquor. In other words, when carrying the present invention into practice, the impregnation of the wood is eifected so completely and rapidly that it is possible to start almost immediately with the digesting temperature required for dissolving the lignin without endangering the resulting fibers.

Broadly stated, the invention contemplates filling a closable digester with fibrous material such as wood chips and then with digesting liquor such as sulfite liquor. After closing the digester completely, the digesting liquor is completely withdrawn and the air occupying the space betwen the adjacent chips and the intra-cellulose space is withdrawn with the creation of a vacuum in the digester. After the withdrawal of the digesting liquor and practically all of the air,

the dige'stingliquor is introduced and the digestion is carried out to the desired extent. It has been found that in this process the liquor im-' mediately penetrates into the interior of the deaerated and de-gassed wood chips when the digester is refilled. In this manner, practically an instantaneous impregnation of the wood chips and wood fibrous material with digesting liquor is accomplished.

According to the present invention, a digester may be used alone in conjunction with the digesting liquor to perform the function of a vacuumprodueing pump. In other words, the shell of the digester may be compared with a cylinder of a pump and the digesting liquor which is withdrawn from the digester may be compared with the piston of a pump. It will readily be appreciated that the lowering of the level of liquor in the digester creates a vacuum and causes the escape of air and gas from the digester and the wood chips in a safe manner. The digestion process is thus accelerated. If desired, a further acceleration of the impregnation process may be effected by reintroducing the digesting liquor into the digester at higher temperatures, for example, temperatures in. the zone of, about C. or so.

In carrying out the present process in practice,- the cover on the top of the digester may be held open while the digestingliquor is reintroduced. In this manner, the reintroduced liquor acts as a piston and pushes air and gas from the digester. In some instances, it may be desirable to conduct the'mixture of air a d 8 8 withdrawn from the top of the digester to a recovery system for'absorption of gases, particularly sulfur dioxide.

In conducting the process, the top of the digester may be subjected to vacuum in order to facilitate the sucking off of the air and gas. For instance, an ejector or other appropriate vacuum-producing apparatus may be connected with the top part of the digester by means of; a pipe or other suitable conduit to suck the air and gas therefrom. For instance, the liquor which is withdrawn from the bottom of the digester may be caused to fiow through an ejector which connected to the top of the digester.' In this manner, you produce a double vacuum effect.

As a result of extensive tests, it has been demonstrated that a higher concentration of digesting liquor. may be employed. When a higher concentration is used, it has been found that only a smaller quantity of digesting liquor is needed than in the case of conventional digesting processes. In this manner, a saving of digesting liqnor is effected in addition to heat. It is believed that the relatively rapid impregnation and the uniform digestion of the fibers which are com pletely protected by the impregnating liquor makes this possible.

Experiments have shown that it is possible after I the impregnation of the fibrous material to immediately start the cooking or digestion at about 100 C. or so. It is believed that this is possible because the impregnation is so complete that endangering the cellulose fibers does not occur.

As the digestion of the fibrous material takes place in almost all parts of the wood chips at the same time, a real shortening of cooking or.

digesting may be effected. The process produces uniform cellulose with an extraordinary saving of cellulose fibers and with the use of a relatively small quantity of digesting liquor and with a relatively small consumption of heat.

For best results, it is essential that the digesting liquor is drained completely from the digester in order that practically every part of the fibrous material is exposed to a vacuum. The subsequent impregnation occurs uniformly throughout practically every part of the wood chips. In withdrawing the liquor from the closed digester it preferred to effect the withdrawal in such Y a manner that the withdrawn liquor can run from the digester under the influence of its own weight. Under'these conditions, an absorbing container or storage reservoir is used into which the withdrawn liquor is conducted. The storage tank is located at a point lower than the bottom of the digester. Of course, the withdrawal of liquormay be effected by the use of pumps or other improved apparatus.

Although a rather constant vacuum is produced in the digester by the withdrawal of liquor itself, means may be employed for controlling, regulating or equalizing the vacuum. These modifications and variations, of course, are to'be considered within the purview and scope of the present invention, as those skilled in the art will readily understand.

. Referring to Fig. 1, the reference character 1 designates a pulp digester or a container. An

inlet line 2 is provided for conducting digesting a 12 and 13 are provided. A pipe line ll'connects the top of the digester with the ejector '1.

The operation of the foregoing apparatus is obvious to those skilled in the art. It will be suflicient to point out that digester 1 is charged with wood chips or other fibrous material and then is filled with digesting liquor such as sulfide liquor. In filling the digester, of course, valves 8 and 9 are opened so that liquor may passfrom pipe 2 to pump 3 and thence to the digester 1 through pipes 4 and 5. After filling the digester,

valves 8 and 9 are closed and valves 12 and 13 are opened as well as valve 10. The liquor withdrawn from digester 1 is passed through ejector 'Z and is conducted to a storage tank (not shown). In emptying the digester, the liquor creates a vacuum and withdraws air and gas from between the wood chips and between the cells within the chips. In addition, the operation of ejector 7 effects a vacuum in pipe 11 and the top of digester and withdraws further amounts of air and gas. When the air and gas has been practically completely removed, from the digester and from the intracellulose space, the liquor isintroduced into the digester and the cooking process is started. As pointed out hereinbefore, the cooking process may be started'at a relatively high temperature, say about 100 C. or so.

In some instances, it may be desirable to use a modified apparatus shown in Fig. 2. In this modified arrangement, many pieces of apparatus are the same as in Fig. 1 and, consequently, the same reference characters will be used in refer-. ring to the same pieces of apparatus.

It will be observed that a plurality of digesters are connected in parallel. Pipe line is connected to the bottom of each digester land then to pump 3 and ejector '7. The filling mouths or' openings 15 at the tops of the digesters are connected together by means of a pipe line or conduit 16. A

valve 17 is provided at the junction where pipe line 16 is connected to theffilling mouths 15. Above pipe line 16 is an auxiliary container 14.

This container is connected by pipe 11 to ejector '7 in the same manner as the top of digester 1 in Fig. 1 was connected to the ejector. A pipe line. 18 extends fromthe top auxiliary container 14 into a storage reservoir 19:

The arrangement shown in Fig. 2 is operated in accordance with the same principle underlying the operation of the apparatus illustrated in Fig. 1. Thus, the digester is completely filled with chips in the usual way. This may be accomplished in any suitable manner but is preferably I effected with a mechanical filling apparatus so .filled with liquor but that the highest compactness of the charge may be reached. After filling the digester with chips ordinary cooking liquor is introduced into the digester. In mills where the cooking liquor is preheated, it is advisable to take for the first charge cold liquor having a temperature of about 25 C.

' to about 357 C. Not only are all of the digesters thev auxiliary "container 14 is filled to overflowing. Any surplus liquor is carried to the storage tank 19 by means of pipe line 18. The valve in pipe line 18 adj acent to, the auxiliarycontainer is shut oil'and'allof the digesters are closed; The first digester is then emptied,- through pipe line 5, pump 3, and ejector linto. storage tank 19. In emptying the digester the 14 is emptied and a vacuum auxiliary container is created. This assists in obtaining a higher pregnation of the vacuum in the digester. The emptying of the digester creates a. vacuum and causes the withdrawal of air and gas between the wood chips and between the wood fibers. The other digesters pump 3 through ejector 7.. As the suction side j of this ejector is connected to the top of auxiliary container 14 by means of pipe line 11, air and gas are removed from the top of the auxiliary con-.

tainer simultaneously. with the discharge of liquor and the removal of air and gas from the digester. In carrying out this process, it has been observed that $02 gases escape with the air and due to the than air they tend to settle to the bottom, whereas the air floats to the top. In consequence, the air tends to rise into auxiliary container 14 and the S03 gases tend to .sink in the digesters.

When the digesters are emptied, the cooking liquor is forced into them again. Either the same liquor which was withdrawn may be used or prewith a preheating apparatus. In the latter case the efliciency of the impregnation is considerably increased. The second feed of liquor to the diconsequently, the operation is achieved rapidly. Thedigester is preferably filled to such an extent with liquor that the quantity fed is about 16 to about 18% less than the total liquor capacity of the digester; The liquorlevel gauge on the digesterpermits an exactregulation of the liquor shaped in any suitable manner for connecting pipe 16. 'When an apparatus of the foregoing construction is used, a relatively high vacuum may be produced in the auxiliary container (for ex ample 500 millimeters iary container may be made of any appropriate material. For instance, the vessel or container may be made vided with a brick lining. Ordinarily, the auxiliary container is only exposed-to relatively low pressures such as 1.5 atmospheres gauge pressure.

In discharging the digesters, the liquor which sucks the air and gas is conducted to storage tank 19. In this storage tank, ,the SO: gases are absorbed in the liquor. bubbles through the liquor and is released at the topof storage tank 19. may be dnterposed between ejector"? and the storage tank in order to force the liquor and gases into the storage tank. By usingIthe foregoing procedure still greater uniformity of imwood chips or cellulose-containing fibrous material is accomplished in all parts'of the digesters. the present invention provides 'a process in which both the preliminary cooking andthe cooking time proper can be considerably shortened. In addifact that the SOzgases are heavier of mercury) The auxil- It will be observed that digesters may heated liquor may be used if the mill is equipped gester is carried out under a'high vacuum and,

of a relatively thin sheet iron prov The undissolved air, etc.,' 7'

If desired, another pump 55 containing fibrous material.

taining the fibers in a condition of maximum solidity. When applying the process to a digester .-having a net capacity, for example, of about 225 cubic meters, about 30-meters were required for 5 drawing off the liquor for evacuating purposes.

The filling of the second batch of liquorinto the digester required about 20 minutes. The impregnation took about one hour while the shortening of the cooking cycle amounted from about 3 to about 5 hours. In certain test, a cooking cycle of about 6 hours was realized, whereas the cooking cycle in the same mill before the introduction of the present process amounted to about 13 to- 14 hours. In other words, by the use of the 15 present invention the time of the cooking cycle is reduced one-half.

It is also to-be observed that in the old impregnating processes the impregnation of the chips proceeded very slowly. When the cellulose fibers were not soaked with liquor they were discolored brownat a temperature of about 105 C. It was, therefore, necessary to extend'the preliminary cooking period a comparatively long time, for instance, from about 5 to about 6 hours. In view of the tact that during the preliminary cooking period the liquor penetrates very slowly into the wood chi there was, of course, an uneven attack of the wood, inasmuch as the fibers on the front sides were attackedbefore the ones at the middle of the-chip. There been found a marked difference between the solidity of the fibers first attacked in comparison with those which were last attacked. Moreover, the uneven attack of digestion further entails a partial destruction or deterioration of. the fibers firstattacked due to the fact that they cannot be discharged from the digester immediately after better strength or solidity in the fibers is obtained.

50 Furthermorait is to be noted that the present invention-may be used for other materials than wood. These other materials may be deaerated and de'gasified in the same manner, as described present invention provides /n' 3 top of ai digester, reintroducing liquor into saidhiester, and effecting digestion of the fibrous material.

"'3. The process of digesting wood and other cellulose-containing fibrous material in a clos- 5 able digester which comprises introducing fibrous material into the digester, completely filling the digester with liquor, discharging the liquor from the bottom of the digester to create. a vacuum and .to withdraw air and gas between the pieces 10 of the fibrous material and within the fibrous material, passing the withdrawn liquor through an ejector connected to the topof the digester v for sucking ofl air. and gas, re-introducing liquor into said digester, and efiecting digestion 15 of the fibrous material. 1

4. The process of digesting wood and other cellulose-containing fibrous material in a closable digester which comprises introducing fibrous material into the digester, completely filling the di- 20 gester with liquor, discharging the liquor. from the bottom of the digester to create a vacuum and to withdraw air and gas between the pieces of the fibrous material and within the fibrous material, re-introducing liquor' into said digester, 25'

opening the top of the digester while re-introducing the liquor, and efiecting digestion of the fibrous material. g 5. An apparatus for deaerating and degasifying' material especially of a fibrous nature which comprises a digester, a discharge pipe connected to the bottom thereof. an ejector connected to'said discharge pipe and a pipe'connecting the suction -port of said ejector with the top of said digester.

6. An apparatus for deaerating and degasifye 35 ing material especially of a fibrous nature which comprises a digester, a discharge pipe connected to the bottom thereof, a pump forwithdrawing and reintroducing liquor from said digester, an

ejector connected to said discharge pipe of said 40 pump, and a pipe connecting the suction port of said ejector with the top of said digester.

7. An apparatus for deaerating and .degasifying material especially of a fibrous nature which comprises a digester, an auxiliary container connected to the top of said digester, a discharge pipe connected to the bottom thereof, an ejector connected to said'di'scharge pipe, a pipe connecting the suction port of said ejector with the topof said auxiliary container, a storage tank connected to said ejector for receiving the withdrawn liquor, air and gas, and a pipe line connecting the top of said auxiliary container with said storage heretofore in connection with wood and cellulosetank I cl 1. The process of digesting wood and other cellulose-containing fibrous material in a closable digester which comprises introducing fibrous mitterial into the digester, completely, filling the digester with'liquor, discharging the liquor from the bottom of the digester to create avacuum and to withdraw air and gas between the pieces'of the fibrous material and within the fibrouslmaterial ing digestion of the fibrous material. V

2. The process of digesting woodand other cellulose-containing fibrous material in a closable reintroducing liquor into said digester, and effectdigester which comprises introducing fibrous ma.

terial into. the digester, completely filling the digester with liquor, discharging the liquor from the bottom of the digester to create a vacuum and e to' withdrawair and gas between the, pieces of the fibrous material and within the fibrous material.

hile sucking air and gas simultaneously from the 8. An apparatus for deaerating and degasify- 65 ing material especially of a fibrous nature which comprises a digester, an auxiliary container. connected to the top of said digester,,a discharge pipe connected to. the bottom thereof, a pump for withdrawing and reintroducing liquor from 60 said digester, an ejector connected to said discharge pipe, a'pipeconnectingthe suction port of said ejector with the top of said a container, a storage tank connected to said ejector forreceiving the withdrawn liquor, air andgas, and a pipe line connecting the top of said auxiliary container with said storage tank. 9. The apparatus set forth in ciaim 7 in which the auxiliary container has the form of a cylinder '10 having a height several times the diameter thereof.. 1

10. 'Ihe apnaratus set forth in claim 8 in which a second liquor p p is located between the ejector and the storage 11. An apparatus for deaerating and degasitying material especially of a fibrous'nature which comprises a plurality of disasters connected in parallel, a discharge pipe connecting to the hottom, of each digester, a connecting pipe associated with the top of each digester, an auxiliary tank connected to said pipe line associated with the tops of the digesters, a pump in said discharge pipe, an ejector operatively associated with said pump, a pipe line connecting the suction port or said adjuster with the top oi-the auxiliary container, a storage tank for receiving liquor, air and gas from the ejector, and a pipe line connecting the top of the auxiliary container with said storage tank.

, O'I'IO KREISSLER. 

